Butyl rubber is understood to be a copolymer of an isoolefin and at least one copolymerizable monomer. Commercial butyl rubbers comprise a major portion of isoolefin and a minor amount, usually not more than 2.5 mol %, of a conjugated multiolefin. One example of butyl rubber is poly(isobutylene-co-isoprene), or IIR, which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene.
Butyl rubber is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmann's Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295.
Canadian Patent No. 2,418,884 and Canadian Patent Application No. 2,458,741 describe the preparation of butyl rubbers which have high multiolefin content. Specifically, Canadian Patent No. 2,418,884 describes the continuous preparation of IIR with isoprene levels ranging from 3 to 8 mol %.
Functionalization of butyl rubber is of great interest due to its potential applications in technology areas such as surface modification, adhesion, drug delivery, compatibilization of polymer blends, and motor oil and fuel additives, and in providing clean cured products without contaminant leaching and/or side products.
One conventional process for functionalization of butyl rubber is halogenations to produce reactive halides. Conventional butyl rubber halogenation processes are described in, for example, Ullmann's Encyclopedia of Industrial Chemistry (5th completely revised Ed., edited by Elvers, et al., volume A231) and Rubber Technology (3rd Ed., edited by Maurice Morton, Chapter 10, particularly pp. 297-300) (Van Nostrand Reinhold Company© 1987). A further example is provided in Canadian Patent Application No. 2,575,652 entitled “Method of Halogenating Butyl Rubber Without Acid Neutralization Agents”, which is incorporated herein by reference in its entirety.
In Ojha et al. Macromolecules, 41, 3832-3841, 2008, syntheses of end-functional polyisobutylenes (PIB), including azide-functional PIB, are disclosed. However, a maximum of one azide group is provided for each polymer chain, which limits the use of the azide-functional PIB for functionalization of the polymer.
The need exists for butyl rubber derivatives having versatile functional groups.